Ignition compositions and device



United States Patent Ofi 3,094,933 Patented June 25, 1963 ice 3,094,933 IGNITION COMPOSITIONS AND DEVICE David T. Zebree, Kingston, N.Y., assiguor to Hercules Powder Company, Wilmington, DeL, a corporation of Delaware No Drawing. Filed Dec. 30, 1960, Bar. No. 79,529 12 Claims. (Cl. 102-28) This invention relates to improved lead-selenium, leadtellurium and lead-selenium-tellurium ignition compositions which contain a diatomaceous earth component as an agent for imparting characteristics thereto. In one as pect this invention relates to such ignition mixtures exhibiting improved resistance to ignition by friction, and improved voltage breakdown properties. In another aspect this invention relates to lead-selenium, lead-tellurium and lead-selenium-tellurium ignition mixtures containing, as an additive component, siliceous skeletons of microscopic aquatic plants, and which, when compressed, exhibit burning rate characteristics of compressed leadselenium, lead-tellurium and lead-selenium-tellurium ignition mixtures but which are characterized by voltage breakdown properties markedly superior to those of the latter. In still another aspect this invention relates to electric blasting caps containing a compressed ignition charge of lead-selenium, lead-tellurium or lead-selenium-tellurium improved by the presence of a diatomaceous earth component.

Lead-selenium, lead-tellurium and lead-seleniumaeilurium mixtures have been utilized for some time in the explosives art as ignition charges in electric blasting caps. Lead-tellurium ignition mixtures are charaterized by burning times significantly longer than those of lead-selenium mixtures so that these compositions and their mixtures afford a selection of burning time over a rather broad range.

Lead-selenium and lead-tellurium ignition mixtures exhibit particularly good burning time characteristics when confined, i.e., when under compression, particularly as regards uniformity of burning time. This is of especial importance in series or delay firing inasmuch as maximum degree of uniformity of firing time is necessary in order to set the requisite sequence. However, these ignition mixtures, confined, particularly lead-selenium, are each characterized by quite low voltage breakdown properties which, of course, markedly limit the conditions under which they can be used.

Both loose and compressed charges of lead-selenium, lead-tellurium and mixtures thereof are quite sensitive though to friction and require, therefore, special care and handling to avoid the hazards inherent in high frictionsensitive charges.

This invention is concerned with lead-selenium, leadtellurium and iead-seleuium-tellurium ignition mixtures, or charges, each containing a diatomaceous earth as an added component and characterized by a voltage breakdown higher, and friction sensitivity lower, than those characteristics of lead-selenium, lead-tellurium or leadselenium-tellurium alone.

In accordance with the invention, lead-selenium, leadtelluriurn and lead-selenium-tellurium ignition mixtures are provided which contain from'OA to 16 weight percent of a diatomaceous earth characterized by an average particle size within the range of from 0.020 to 4 microns, as an agent which imparts improved voltage breakdown and friction sensitivity properties to the resulting composition.

Further in accordance with the invention, electric blasting caps are provided in which the ignition charge is an ignition mixture of lead-selenium, lead-tellurium and mixtures thereof containing from 0.4 to 16 Weight percent of a diatomaceous earth characterized by an average particle size within the range of from 0.020 to 4 microns and confined at a density of from 2.6 to 4.5 g./cc.

The invention is illustrated with reference to the firing and sensitivity tests described in the following examples. Each of the blasting caps tested comprised a bronze shell 2%" in length by a diameter of 0.256 to 0.261 (tapered), 0.40 gram of PETN (pentaerythritol tetranitrate) pressed in the end of the shell to occupy of the shell length as the base charge, 0.30 gram of diazodinitrophenol pressed to 2,000 pounds per square inch superposed on the base charge as the primer, a metal capsule imbedded in the primer to provide of the primer length under the capsule and & above the capsule, the ignition charge, one gram, being superposed on the primer and further characterized as specifically indicated in each of the examples. In all instances a Bakelite ignition plug was utilized with the bridgewire imbedded in the ignition charge. Each cap contained an asphalt waterproofing layer above the ignition plug and was topped with sulfur. The lead-telluriurn and lead-selenium ignition charge components were in stoichiometric proportions in all instances, i.e., Pb:Se=72.4/27.6 and Pb:Te=61.9/38.l. In those tests made employing a delay fuse, the fuse composition, i.e., between the ignition and primer charges, was a barium peroxide-selenium mixture, 70/30.

EXAMPLE 1 A series of electric blasting caps above described was tired employing loose lead-selenium, pressed lead-selenium and pressed lead-selenium/Snow Floss as shown in the following tabulation.

l 10 shots for each ignition charge.

The data of Table I demonstrate the advantage of pressed lead-selenium over loose lead-selenium, as an ignition mixture, in respect to uniformity of burning time as shown by the relatively narrow spread values observed and, accordingly, the advantages offered by lead-selenium ignition mixtures when in compressed form. The table further demonstrates pressed lead-selenium/ Snow Floss to also exhibit a marked improvement in uniformity in burning time, again as shown by the observed spread values. Accordingly then, pressed lead-selenium is markedly advantageous over the unpressed, or loose, mixture in those firings of series and delay type. However, pressed leadselenium ignition charges, as demonstrated hereinafter, are characterized by quite low voltage breakdown values whereas the pressed iead-selenium/Snow Floss charges exhibit markedly higher breakdown characteristics so as to be greatly advantageous over the pressed lead-selenium (alone) charges.

. EXAMPLE 2 Tests similar to those of Example 1 were repeated except that the blasting cap in each instance was a delay containing the barium peroxide-selenium fuse as a core in a lead tube long as the delay fuse. The firing data are set forth in the following tabulation.

3 Table II 1 Timing Data, Milliseconds (ms) Pb-Se Pb-So Pressed (Loose) at 2,000

lb./sq. in.

Ph Se/Snow Floss. 97/3 (Pressed at 2,000 lbJsq. in.)

Average burning time s. 323 310 327 Spread in burning time 59 18 16 l 10 shots [or each ignition charge.

EXAMPLE 3 The following tabulation summarizes data observed from shots made at various degrees of compression of the igntion charge, for lead-selenium and lea-d-selenium/ Snow Floss and demonstrate that the narrow range of burning time spread values characteristic of lead-selenium/Snow Floss ignition charges are obtained over a wide range of confinement pressures.

Table III 1 Pb-Se/Snow Floss, 97/3, Timing Data Pb-Se Pressure on Ignition Powder Average Spread Average Spread None (loose) 111 500 lbjsq. in 2,000 lb./sq. in 55 3,000 lbJSq. in 49 1 5 shots for each ignition charge.

EXAMPLE 4 The voltage breakdown characteristics of lead-selenium mixtures, with and without Snow Floss, are demonstrated in the following tabulation.

Table IV Voltage Breakdown (Shunt Pressure on Ignito Shell) tion Powder (lo/sq. in.)

Ignition Composition Min. Value, volts Tested Pb-Se/Snow Floss 97/3 o intravenous-1mm EXAMPLE 5 Table V Friction Mixture (Loose) Sensitivity (3 kg wt.), centimeters Ph-Se 8 Pb-So/Snow Floss, 9773.. 12

EXAMPLE 6 In the following tabulation are reported results of firing tests employing lead-tellurium ignition mixtures with and without Snow Floss:

Table VI Voltage Ignition Mixture (Compressed No. of Breakdown at 3,000 ill/Sq. in.) Shots (v.) Shunt to Shell Pb-Te 10 10 Pb-Te/Snow Floss, 97/3 10 100-125 EXAMPLE 7 Series firing current characteristics of lead-selenium alone and containing various amounts of Snow Floss are shown in the following tabulation which demonstrates that even with a substantial dilution of the ignition mixture with the siliceous material component, ignition sensitivity by the heat generated from the bridgewire is not appreciably affected.

Although it is within the scope of the invention to utilize any ignitable proportions of lead, selenium and tellurium in my compositions, lead is generally present in molar proportion to selenium and/or tellurium in the range of from about 0.2:1 to 3.4:1. The composition based only on the lead-selenium and/or -tellurium components is generally within the range of from about 35 to 81 percent lead and from about 19-65 percent selenium and/or tellurium, the overall diatomaceous earth content being from about 0.4 to 16 weight percent.

The amount of diatomaceous earth material employed as a component of the ignition charge is, of course, dependent upon the problem at hand, being often, however, in the range of about 0.5 to 6 weight percent. Thus, when utilizing the diatomaceous earth as a component of a compressed lead-selenium or compressed lead-tellurium ignition composition, the amount generally employed is in the order of about 2 to 4 weight percent whereas when utilized as a component of a loose lead-tellurium or lead-selenium mixture to improve friction sensitivity characteristics, the amount generally employed is in the order of about 0.5 to 2 weight percent. Of course, dependent upon the specific proportions of lead and selenium and/or tellurium utilized, proportions outside the above ranges, in each instance, may be advantageously employed.

The ignition charge compositions of this invention are generally pressed into the cap at a pressure of at least about 500 p.s.i.g. in order that an appreciable improvement in voltage breakdown properties is obtained, i.e., in contrast to the small improvement in that respect that would be obtained at lower pressures. However, de-

pendent upon the particular assembly and the problem at hand, lower confinement pressures can be employed.

In the fabrication of an electric blasting cap assembly of the invention, the base charge is pressed into the bottom of the shell under pressure, say in the order of about 2000-3000 p.s.i.g. Exemplary base charges are pentaerythritol tetranitrate, trinitrotrimethylenetriamine, and trinitrophenylmethylnitrarnine. The primer charge is similarly pressed into the shell superposed on the base charge, exemplary primers being lead azide, diazodinitrophenol and mercury fulminate. Any conventional pin means for effecting compression can be utilized in placing these charges in the shell. In fabricating a delay blasting cap, the delay fuse is disposed as a core in a lead tube, the latter snugly fit into the shell and pressed down upon the primer charge, again employing conventional pin means if desired. Barium peroxide-selenium, barium peroxide-tellurium and barium peroxide-seleniumtellurium delay fuse compositions are advantageously employed. The pressed ignition charge of the invention can be pressed into position by any suitable means. However, it is preferable generally to employ as the ignition assembly a plastic ignition plug through which the pin wires extend and connect it and terminated ends with the bridgewire and to insert the assembly into the shell and then press the assembly, bridgcwire first, onto the ignition composition by application of pressure on the top side of the plug so as to force the plug onto the ignition mixture to obtain an over-press, i.e., to press the ignition composition to the desired degree, generally at a pressure of from 500-3000 p.s.i. to obtain the desired density increase. Conventional waterproofing, generally an asphalt layer, superposed on the ignition plug together with a sulfur topping, is advantageously employed to complete the assembly.

Independently of the manner in which the pressed ignition charge of the invention is placed into position, I have found that in order to obtain the degree of improvement in voltage breakdown, generally desired, it is necessary that the density of the ignition charge under confinement be in the order of from about 2.6 to 4.5 g./cc.

The diatomaceous earth materials employed in the practice of the invention are characterized by an average particle size in the range from 0.020 to 4 microns. These materials are natural occurring siliceous materials formed from siliceous skeletons of microscopic aquatic plants called diatoms. Exemplary are keiselguhr, Celite and Snow Floss. Celite, a trade name, designates a soft earthy formation of the above said siliceous skeletons. Snow Floss is a trade name given to Celite when in the highly purified state such as to be substantially white. The Snow Floss component, in all the working examples herein, was characterized by a particle size within the above said 0.020-4 range.

The ignition charges of this invention, particularly confined to a density within the above described range, are particularly advantageously applied to delay electric blasting caps in view of the maximum degree of uniformity of firing time that they provide and which is required in order to set forth the requisite time sequence. However, the ignition charges are advantageously applied to any firing devices which utilize an electric firing circuit such as the ignition plug-pin wire-bridgewirc assembly above described, the bridgewire always being in direct contact with the said iginition charge, preferably imbedded therein. Instantaneous electric blasting caps and squibs are further exemplary of the now preferred firing devices in which the ignition charge compositions of this invention can be utilized.

The compositions of this invention will burn without the production of any substantial amount of gas and thus will not rupture the cap casing or dislodge the bridgewire upon firing. In preparing a composition of this invention in accordance with one embodiment, the in gredients are reduced to a finely divided form and are then intimately admixed by any suitable procedure. Generally, the average particle size of the lead, selenium and. tellurium components will be in the range of about 1 to 70 microns, although an average particle size outside that range can be utilized if desired. The composition is loaded into any desired form of blasting cap in any usual manner.

In the determination of voltage breakdown referred to herein, the test circuit is connected at one end to the shunted lead wires and at the other end to the cap shell. The voltage across the cap, i.e., shunted lead wires to shell, initially zero, is progressively increased until the resistance across the cap is overcome and the breakdown occurs to permit flow of current across the cap with concomitant drop in voltage. The level at which the voltage drop initially takes place is the voltage breakdown value. The lower the voltage breakdown value, the greater is the susceptibility of the cap to accidental initiation by stray currents.

As will be evident to those skilled in the art, various modifications can be made or followed, in the light of the foregoing disclosure and discussion, without departing from the spirit or scope of the disclosure or from the scope of the claims.

What I claim and desire to protect by Letters Patent is:

1. As a new composition, an ignition mixture selected from the group consisting of lead-selenium, lcad-tellurium and lead-selenium-tellurium and of from 0.4 to 16 weight percent of a diatomaceous earth characterized by a particle size of from 0.020 to 4 microns.

2. A composition of claim 1 containing lead in a mole ratio to selenium within the range of from 0.2:1 to 3.4: l.

3. A composition of claim 1 containing lead in a mole ratio to tellurium within the range of from 0.2:1 to 3.411.

4. A composition of claim 1 containing as said diatomaceous earth, siliceous skeletons of microscopic aquatic plants in a sufiicientiy purified state as to be substantially White.

5. A composition of claim 1 wherein said selenium and said tellurium are each present in substantially stoichiometric proportions with said lead.

6. A composition of claim 4 wherein said ignition mixture is lead-selenium and from 0.4 to 6 percent of the said diatomaceous component.

7. A composition of claim 4 wherein said ignition mixture is lead-tellurium and from 0.4 to 6 percent of the said diatomaceous component.

8. A composition of claim 11 wherein said composition is further characterized by a density of from 2.6 to 4.5 g./cc.

9. In an electric firing device having in combination an ignition charge, a resistance wire in contact with said ignition charge and means for passing an electric current through said resistance wire to develop heat for initiation of burning of said ignition charge, the improvement which comprises as said ignition charge an ignition mixture selected from the group consisting of lead-selenium, leadtellurium and lead-selenium-tellurium containing from 0.4 to 16 weight percent of a diatomaceous earth having an average particle size within the range of from 0.020 to 4 microns.

10. In an electric blasting cap containing a dctonatable base charge and a primer charge for initiating said base charge upon being heated, and an ignition charge for generation of heat, from burning of same, to cause initiation of said primer, the improvement providing as said ignition charge an ignition mixture of lead and selenium and from 0.4 to 6 weight percent of a siliceous material consisting of skeletons of microscopic aquatic plants characterized by a particle size within the range of about 0.020 to 4 microns.

ll. In an electric blasting cap of claim 10, a delay fuse disposed intermediate said ignition charge and said primer in operative relation with said ignition charge and said primer to burn and thereby initiate said primer in response to burning of said ignition charge, and wherein said ignition charge is confined and characterized by a density in the range of from about 2.6 to about 4.5 grams per cc.

12. A delay blasting cap of claim 11 wherein said siliceous material is in a suceinflitly high state of purity as to be substantially white.

References Cited in the file of this patent UNITED STATES PATENTS 

10. IN AN ELECTRIC BLASTING CAP CONTAINING A DETONATABLE BASE CHARGE AND A PRIMER CHARGE FOR INITIATING SAID BASE CHARGE UPON BEING HEATED, AND AN IGNITION CHARGE FOR GENERATION OF HEAT, FROM BURNING OF SAME, TO CAUSE INITIATION OF SAID PRIMER, THE IMPROVEMENT PROVIDING AS SAID IGNITION CHARGE AN IGNITION MIXTURE OF LEAD AND SELENIUM AND FROM 0.4 TO 6 WEIGHT PERCENT OF A SILICEOUS MATERIAL CONSISTING OF SKELETONS OF MICROSCOPIC AQUATIC PLANTS CHARACTERIZED BY A PARTICLE SIZE WITHIN THE RANGE OF ABOUT 0.020 TO 4 MICRONS. 